System and method of qos-based channel selection for wlan access points or stations

ABSTRACT

A system comprises a candidate channel assessment module for obtaining at least one AC-specific channel suitability metric for each of two different channels, and for using the AC-specific channel suitability metrics to determine a channel suitability index of each of the two different channels; a channel selection module for using the channel suitability index to select one of the two different channels as a new channel; and a channel setting module for configuring a wireless transceiver to use the new channel.

COPYRIGHT NOTICE

A portion of the disclosure of this patent, document, contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

TECHNICAL FIELD

This invention relates generally to wireless local area networks, andmore particularly provides a system and method of QOS-based channelselection for wireless local area network (WLAN) access points orwireless stations (STAs).

BACKGROUND

As users experience the convenience of wireless connectivity, they aredemanding increasing support. WLANs are now offered by cafes, airports,hotels, businesses, residences, etc. Typical applications over wirelessnetworks include video streaming, video conferencing, distance learning,etc. Because wireless bandwidth availability is restricted, quality ofservice (QoS) management is increasingly important in 802.11 networks.

The original 802.11 media access control (MAC) protocol was designedwith two modes of communication for wireless stations (STAs). The firstmode, Distributed Coordination Function (DCF), is based on Carrier SenseMultiple Access with Collision Avoidance (CSMA/CA), sometimes referredto as “listen before talk.” A wireless station (STA) waits for a quietperiod on the network and then begins to transmit data and detectcollisions. The second mode, Point Coordination Function (PCF), supportstime-sensitive traffic flows. Using PCF, wireless access points (APs)periodically send beacon frames to communicate network identificationand management parameters specific to the wireless local area network(WLAN). Between beacon, frames, PCF splits time into a contention period(CP) where the STAs implement a DCF protocol, and a contention-freeperiod (CFP) where an AP coordinates access by the various STAs based onQoS requirements.

Because DCF and PCF do not differentiate between traffic types orsources, IEEE proposed enhancements to both coordination modes tofacilitate QoS. These changes are intended to fulfill critical servicerequirements while maintaining backward-compatibility with current802.11 standards.

Enhanced Distributed Channel Access (EDCA) introduces the concept oftraffic categories (or access classes or traffic classes or ACs). UsingEDCA, STAs try to send data after detecting that the wireless medium isidle for a set time period defined by the corresponding AC. Ahigher-priority AC will have a shorter wait time than a lower-priorityAC. While no guarantees of service are provided, EDCA establishes aprobabilistic priority mechanism to allocate bandwidth based on ACs.

The IEEE 802.11e EDCA standard provides QoS differentiation by groupingtraffic into tour ACs, i.e., voice (VO), video (VI), best effort (BE)and background (BK). Each transmission frame from the upper layers bearsa priority value (0-7), which is passed down to the MAC layer. Based onthe priority value, the transmission frames are mapped into the four ACsat the MAC layer. The VO AC has the highest priority; the VI AC has thesecond highest priority; the BE AC has the third highest priority; andthe BK AC has the lowest priority. Each AC has its own transmissionqueue and its own set of AC-sensitive medium access parameters—thearbitration interframe space (AIFS) interval, contention window (CW,CWmin and CWmax), and transmission opportunity (TXOP). Trafficprioritization uses the medium access parameters to ensure that a higherpriority AC has relatively more medium access opportunity than a lowerpriority AC.

Generally, in EDCA, AIFS is me time interval that a STA must, sense thewireless medium to be idle before invoking a backoff mechanism ortransmission. A higher priority AC uses a smaller AIFS interval. Thecontention window (CW, CWmin and CWmax) indicates the number of backofftime slots until the STA can attempt another transmission. Thecontention window is selected as a random backoff number of slotsbetween 0 and CW. CW starts at CWmin. CW is essentially doubled everytime a transmission fails until CW reaches its maximum value CWmax.Then, CW maintains this maximum value CWmax until the transmissionexceeds a retry limit. A higher priority AC uses smaller CWmin andCWmax. A lower priority AC uses larger CWmin and CWmax. The TXOPindicates the maximum duration that an AC can he allowed to transmitframes after acquiring access to the medium. To save contentionoverhead, multiple transmission frames can be transmitted within oneTXOP without additional contention, as long as the total transmissiontime does not exceed the TXOP duration.

To reduce the probability of two STAs colliding, because the two STAscannot hear each other, the standard defines a virtual carrier sensemechanism. Before a STA initiates a transaction, the STA first transmitsa short control frame called RTS (Request To Send), which includes thesource address, the destination address and the duration of the upcomingtransaction (i.e. the data frame and the respective ACK). Then, thedestination STA responds (if the medium is free) with aresponsive-control, frame called CTS (Clear to Send), which includes thesame duration information. All STAs receiving either the RTS and/or theCTS set a virtual carrier sense indicator, i.e., the network allocationvector (NAV), for the given duration, and use the NAV together with thephysical carrier sense when sensing the medium as idle or busy. Thismechanism reduces the probability of a collision in the receiver area bya STA that is “hidden” from the transmitter STA to the short duration ofthe RTS transmission, because the STA hears the CTS and “reserves” themedium as busy until the end of the transaction. The durationinformation in the RTS also protects the transmitter area fromcollisions during the ACK from STAs that are out of range of theacknowledging STA. Due to the fact that the RTS and CTS are short, themechanism reduces the overhead of collisions, since these transmissionframes are recognized more quickly than if the whole data transmissionframe was to be transmitted (assuming the data frame is bigger thanRTS). The standard allows for short data transmission frames, i.e.,those shorter than an RTS Threshold, to be transmitted without theRTS/CTS transaction.

With these medium access parameters, EDCA works in the following manner:

Before a transmitting STA can initiate any transmission, thetransmitting STA must first sense the channel idle (physically andvirtually) for at least an AIFS time interval. If the channel is idleafter the initial AIFS interval then the transmitting STA initiates anRTS transmission and awaits a CTS transmission from the receiving STA.

If a collision occurs during the RTS transmission or if CTS is notreceived, then the transmitting STA invokes a backoff procedure using abackoff counter to count down a random number of backoff time slotsselected between 0 and CW (initially set to CWmin). The transmitting STAdecrements the backoff counter by one as long as the channel is sensedto be idle. If the transmitting STA senses the channel to be busy at anytime during the backoff procedure, the transmitting STA suspends itscurrent backoff procedure and freezes its backoff counter until thechannel is sensed to be idle for an AIFS interval again. Then, if thechannel is still idle, the transmitting STA resumes decrementing itsremaining backoff counter.

Once the backoff counter reaches zero, the transmitting STA initiates anRTS transmission and awaits a CTS transmission from the receiving STA.If a collision occurs during the RTS transmission or CTS is notreceived, then the transmitting STA invokes another backoff procedure,possibly increasing the size of CW. That is, as stated above, aftereach, unsuccessful transmission, CW is essentially doubled until itreaches CWmax. Alter a successful transmission, CW returns to itsdefault value of CWmin. During the transaction, the STA can initiatemultiple frame transmissions without additional contention as long asthe total transmission time does not exceed the TXOP duration.

The level of QoS control for each AC is determined by the combination ofthe medium access parameters and the number of competing STAs in thenetwork. The default EDCA parameter values used by non-AP QoS stations(QSTAs) are identified in the table of FIG. 1. A TXOP_Limit value of 0indicates that a single MAC service data unit (MSDU) or MAC protocoldata unit (MPDU), in addition to a possible RTS/CTS exchange or CTS toitself, may be transmitted at any rate for each TXOP.

In a point-coordinated access mode, e.g., PCF, a single WLAN includes atleast one AP in communication with one or more STAs. The combination ofthe single AP and its STAs is referred to as a “basic service set” or“BSS.” FIG. 1B illustrates an example BBS network 100, which includestwo BSSs 105 a and 105 b (each generally referred to as a BSS 105), eachcoupled to a computer network 110 such as the wide area network commonlyreferred to as the Internet. In the example shown, the BSS 105 aincludes an AP 115 a and three (3) STAs 120 a. The BSS 105 b includes anAP 115 b and two (2) STAs 120 b. Wireless communication by the STAs 120a of BSS 105 a goes through the AP 115 a. Wireless communication by thestations 120 b of BSS 105 b goes through the AP 115 b. Since mostcorporate WLANs require access to a wired LAN for services (e.g., fileservers, network printers, Internet links, etc.), corporate WLANstypically operate using a point-coordinated access mode.

In a distributed access mode, e.g., DCF, a group of STAs operate in amanner analogous to a peer-to-peer network, in which there is no AP andno single STA is required to function as the AP. The combination of STAsin the ad-hoc network is commonly referred to as an “independent basicservice set,” “independent BSS” or “IBSS.” FIG. 1C illustrates an IBSS150 having four (4) STAs 155. As shown, each STA 155 is capable ofcommunicating directly or indirectly with the other STAs 155 of the IBSS150. IBSS 150 is useful when quick and easy setup of a WLAN is desired,where connection to a wired network is not needed (e.g., where servicesmay not be offered, such as in a hotel room, convention center, airport,etc.), and/or where access to a wired network is barred (e.g., forconsultants at a client site). A BSS 105, e.g., BSS 105 a and/or BSS 105b of FIG. 1B, may include an IBSS 150.

It should be appreciated that a WLAN operating using infrastructuremode, ad-hoc mode or a combination of the two can be referred to as aBSS 105.

When two or more BSSs 105 are located proximate to one another and areoperating over the same channel, link quality may deteriorate, e.g., dueto contention among the overlapping BSSs and/or signal interference.Accordingly, it becomes difficult to guarantee QoS over WLANs, e.g., forreal-time multimedia applications. For example, in FIG. 1, if the BSS105 a were located proximate to BSS 105 b, then the BSSs 105 a and 105 bmay interfere with each other.

Systems and methods are needed to improve link quality caused byoverlapping BSSs 105. Example prior art references include:

U.S. Patent/Publ. No. Inventor Issue/Publ. Date US 6,333,937 B1 RyanDec. 25, 2001 US 6,985,461 B2 Singh Jan. 10, 2006 US 6,738,599 B2 Black,et al. May 18, 2004 US 2003/0181211 A1 Razavilar, et al. Sep. 25, 2003US 2004/0264413 A1 Kaidar, et al. Dec. 30, 2004 US 2005/0003827 A1Whelan Jan. 06, 2005 US 2005/0122999 A1 Scherzer, et al. Jun. 09, 2005US 2006/0029023 A1 Cervello, et al. Feb. 09, 2006 Pending Application SNInventor Filing Date U.S. Pat. No. 11/588,778 Zhao Oct. 26, 2006

SUMMARY

In accordance with one embodiment, the present invention provides asystem comprising a candidate channel assessment module for obtaining atleast one AC-specific channel suitability metric for each of twodifferent channels, and for using the AC-specific channel suitabilitymetrics to determine a channel suitability index of each of the twodifferent channels; a channel selection module for using the channelsuitability index to select one of the two different channels as a newchannel; and a channel setting module for configuring a wirelesstransceiver to use the new channel.

The system may include an access point. The access point may communicatewith a wireless station to obtain the at least one AC-specific channelsuitability metric therefrom. The channel assessment module may applythe following equations to generate the channel suitability index (CSI):

CSI=Ψ(LQ,CF)

where Ψ indicates a function defining the relative success intransmitting a packet error free and as an example may be defined as:

Ψ(LQ,CF)=LQ×CF

where LQ indicates link quality and as an example may be defined as:

${LQ} = {\sum\limits_{{ACI} = 0}^{3}\; {\sigma_{ACI}{\Omega ( {\overset{\_}{RSSI}}_{ACI} )}}}$

where σ indicates a weight associated with a particular AC, thesubscript ACI identifies AC index, RSSI indicates a mean received signalstrength indicator, Ω indicates a function defining link robustness. Thefunction Ω may be dependent on the modulation scheme being used. Forexample, assuming binary phase shift keying (BPSK) modulation, it may bedefined as:

${\Omega ( {\overset{\_}{RSSI}}_{ACI} )} = {1 - {\frac{1}{2}{{erfc}( \sqrt{{\overset{\_}{RSSI}}_{ACI}} )}}}$

where erfc(.) indicates a complementary Gaussian, error function, CFindicates contention-faced and as an example may be defined as:

${CF} = {\sum\limits_{{ACI} = 0}^{3}\; {\tau_{ACI}{\Gamma ( {N_{ACI},{CU}_{ACI},{APER}_{ACI}} )}}}$

where τ indicates a weight associated with a particular AC, CD indicateschannel utilization, APER indicates average packet error rate, Nindicates, the number of active STAs, and Γ is a function definingrelative contention faced when trying to gain access to the wirelessmedium and as an example may be computed as:

$\Gamma = {\frac{\{ {( {100 - {CU}_{ACI}} ) + ( {100 - {APER}_{ACI}} )} \}}{2\; N_{ACI}}.}$

The channel selection module may select the channel having the greatestchannel suitability index. The system may include a wireless station,the candidate channel assessment module may include a BSS channelassessment module; and the channel selection module may include a BSSchannel selection module. The system may further comprise a currentchannel assessment module for determining when to initiate the candidatechannel assessment module. The current channel assessment module mayinitiate the candidate channel assessment module when a current channellink quality value fails a threshold test. The AC-specific metric mayinclude an AC-specific link quality metric and an AC-specificcontention-faced metric. The wireless transceiver may implement an IEEE802.11e protocol.

In accordance with another embodiment, the present invention provides amethod comprising obtaining at least one AC-specific channel suitabilitymetric for each of two different channels; using the AC-specific channelsuitability metrics to determine a channel suitability index of each ofthe two different channels; using the channel suitability index toselect one of the two different channels as a new channel; andconfiguring a wireless transceiver to use the new channel.

The method may be operative in an access point. The method may furthercomprise communicating with a wireless station to obtain the at leastone AC-specific channel suitability metric therefrom. The method mayfurther comprise applying the following equations to generate thechannel suitability index (CSI):

CSI=Ψ(LQ,CF)

where Ψ indicates a function defining the relative success intransmitting a packet error free and as an example maybe defined as:

Ψ(LQ,CF)=LQ×CF

where LQ indicates link quality and as an example may be defined as;

${LQ} = {\sum\limits_{{ACI} = 0}^{3}\; {\sigma_{ACI}{\Omega ( {\overset{\_}{RSSI}}_{ACI} )}}}$

where σ indicates a weight associated with a particular AC, thesubscript ACI identifies AC index, RSSI indicates a mean received signalstrength indicator, Ω indicates a function defining link robustness. Thefunction Ω is dependent on the modulation scheme being used. Forexample, assuming binary phase shift keying (BPSK) modulation, it may bedefined as:

${\Omega ( {\overset{\_}{RSSI}}_{ACI} )} = {1 - {\frac{1}{2}{{erfc}( \sqrt{{\overset{\_}{RSSI}}_{ACI}} )}}}$

where erfc(.) indicates a complementary Gaussian error function, CFindicates contention-faced and as an example may be defined as:

${CF} = {\sum\limits_{{ACI} = 0}^{3}\; {\tau_{ACI}{\Gamma ( {N_{ACI},{CU}_{ACI},{APER}_{ACI}} )}}}$

where τ indicates a weight associated with a particular AC, CU indicateschannel utilization, APER indicates average packet error rate, Nindicates the number of active STAs, and Γ is a function definingrelative contention faced when trying to gain access to the wirelessmedium and may be computed as:

$\Gamma = {\frac{\{ {( {100 - {CU}_{ACI}} ) + ( {100 - {APER}_{ACI}} )} \}}{2\; N_{ACI}}.}$

The method may further comprise selecting the channel having thegreatest channel suitability index. The method may be operative in awireless station. The method may further comprise determining when toinitiate the candidate channel assessment module. The method may furthercomprise initiating the candidate channel assessment module when acurrent, channel link quality value fails a threshold test. TheAC-specific metric includes an AC-specific link quality metric and anAC-specific contention-faced metric.

In accordance with yet another embodiment, the present inventionprovides a system comprising means for obtaining at least oneAC-specific channel suitability metric for each of two differentchannels; means for using the AC-specific channel suitability metrics todetermine a channel suitability index of each of the two differentchannels; means for using the channel suitability index to select one ofthe two different channels as a new channel; and means for configuring awireless transceiver to use the new channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a table of a prior art EDCA access class (AC) parameter setfor 802.11g.

FIG. 1B is block diagram of a basic service set (BSS) network, inaccordance with the prior art.

FIG. 1C is a block diagram of an independent basic service set (IBSS),in accordance with the prior art.

FIG. 2 is a block diagram of a BSS network using a point-coordinatedaccess mode and channel control, in accordance with an embodiment of thepresent invention.

FIG. 3 is a block diagram of a channel control module of FIG. 2, inaccordance with an embodiment of the present invention.

FIG. 4 is a block diagram of a channel agent module of FIG. 2, inaccordance with an embodiment of the present invention.

FIG. 5 is a table illustrating example weight assignments for differentaccess classes, in accordance with an embodiment of the presentinvention.

FIG. 6 is a block diagram of an IBSS with channel control, in accordancewith an embodiment of the present invention.

FIG. 7 is a block diagram of an ad-hoc (AH) channel control module, inaccordance with an embodiment of the present invention.

FIG. 8 is a flowchart of a method of controlling channel selection, inaccordance with an embodiment of the present invention.

FIG. 9 is a graph illustrating an example scenario in which channelassessment and control would be helpful, in accordance with anembodiment of the present invention.

FIG. 10 is a graph illustrating a resulting scenario after applyingchannel assessment and control on the example scenario of FIG. 9, inaccordance with a system not implementing the present invention.

FIG. 11 is a graph illustrating a resulting scenario after applyingchannel assessment and control on the example scenario of FIG. 9, inaccordance with an embodiment of the present invention.

FIG. 12 is a graph illustrating an example scenario in which channelassessment and control would be helpful in accordance with an embodimentof the present invention.

FIG. 13 is a graph illustrating a resulting scenario after applyingchannel assessment and control on the example scenario of FIG. 12, inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The following description is provided to enable any person skilled inthe art to make and use the invention; and is provided in the context ofa particular application and its requirements. Various modifications tothe embodiments are possible to those skilled in the art, and thegeneric principles defined herein may be applied to these, and otherembodiments and applications without departing from, the spirit andscope of the invention. Thus, the present invention is not intended tobe limited to the embodiments shown, but is to be accorded the widestscope consistent with the principles, features and teachings disclosedherein.

Embodiments of the present invention exploit AC-specific metrics todetermine channel suitability,. Embodiments of the present inventionexploit AC-specific metrics in conjunction with other relevant generalmetrics to determine channel suitability.

FIG. 2 is a block diagram of a BSS network 200 in a point-coordinatedaccess context, in accordance with an embodiment of the presentinvention. The BSS network 200 includes a first BSS 205 a and a secondBSS 205 b (each generally referred to as a BSS 205), each coupled to thecomputer network 110. The first BSS 205 a includes an AP 215 a and twoSTAs 220 a. The second BSS 205 b includes an AP 215 b and one STA 220 b.The AP 215 a includes a channel control module 225 a. The AP 215 bincludes a channel control module 225 b, which may be the same as thechannel control module 225 a. Each STA 220 a includes a channel agentmodule 230 a. Each STA 220 b includes, a channel agent module 230 b,which may be the same as the channel agent module 230 a. Each of the AP215 a and the AP 215 b may be generally referred to as an AP 215. Eachof the STAs 220 a and STA 220 b may be generally referred to as a STA220. Each of the channel control module 225 a and the channel controlmodule 225 b may generally be referred to as a channel control module225. Each of the channel agent module 230 a and the channel agent module230 b may generally be referred to as a channel agent module 230.

In one embodiment, each channel control module 225 includes hardware,software and/or firmware to enable current channel suitabilityassessment, candidate channel suitability assessment, new channelselection, and new channel configuration. Additional details of thechannel control module 225 will be described below with reference toFIG. 3. Each channel agent module 230 includes hardware, software and/orfirmware to enable current channel suitability assessment, candidatechannel suitability assessment, new channel configuration, and BSSchannel assessment/selection. Each channel agent module 230 will bedescribed below with reference to FIG. 4.

Generally, the channel control module 225 and the channel agent modules230 of the STAs 220 of a BSS 205 cooperate to enable current channelsuitability assessment, candidate channel suitability assessment, newchannel selection, and new channel configuration.

When establishing a new BSS 205, the channel control module 225 andchannel agent modules 230 may initially configure the new BSS 205 tocommunicate over a default channel, over a channel randomly selectedfrom available channels, etc. The channel control module 225 and channelagent modules 230 may assess current channel suitability upon setup, ona periodic basis, at predetermined times, and/or the like, in oneembodiment, the channel control module 225 initiates current channelsuitability assessment hi another embodiment, each channel agent module230 independently assesses current channel suitability (e.g.,substantially continuously, on a periodic basis, etc.), and informs thechannel control module 225 when current channel suitability is below athreshold. Then, the channel control module 225 may initiate candidatechannel suitability assessment and new channel selection.

FIG. 3 is a block diagram, of the channel control module 225, inaccordance with an embodiment of the present invention. The channelcontrol module 225 includes a current channel assessment module 305, acandidate channel assessment module 310, a new channel selection module315, and a new channel setting module 320.

The current channel assessment module 305 includes hardware, softwareand/or firmware to initiate/schedule current channel suitabilityassessment, e.g., upon setup, on a periodic basis, on an event-initiatedbasis, upon request by a STA 120, upon user request, at predeterminedtimes, and/or the like. In one embodiment, the current channelassessment module 305 communicates with the channel agent module 230 ofeach STA 220, e.g., to provide parameters and initiate current channelsuitability assessment. Examples of channel suitability metrics mayinclude mean received signal strength indicator (RSSI), average packeterror rate (APER), noise, signal-to-noise ratio (SNR), and/or the like.In some embodiments, channel suitability assessment may be on anAC-specific basis (not necessarily for all ACs).

In one embodiment, the current channel assessment module 305 includeshardware, software and/or firmware to evaluate channel suitabilitymetrics of the current channel as noted by the AP 215. The currentchannel assessment module 305 determines channel suitability bymeasuring RSSI, noise, SNR, and/or the like, possibly on an AC-specificbasis.

In one embodiment, the current channel assessment module 305 computesMAC layer link quality by inspecting the retry field in the frame headerand counting the number of retries in a given time period T as describedin co-pending U.S. patent application Ser. No. 11/588,788 to Zhao, whichis hereby incorporated by reference. In one embodiment, the currentchannel assessment module 305 may evaluate the retry count on anAC-specific basis.

In one embodiment, the current channel assessment module 305 receivesthe channel suitability metrics from each STA 220. In one embodiment,the current channel assessment module 305 computes averages of thechannel suitability metrics as received from the STAs 315 and asmeasured by the current channel assessment module 305 itself. Thecurrent channel assessment module 305 may compare the channelsuitability metrics against a predefined threshold to determine whethercandidate channel suitability assessment may he needed. In oneembodiment, the current channel assessment module 305 may conduct itsthreshold analysis on an AC-specific basis. The current channelassessment module 305 may weight channel suitability metrics of higherpriority ACs (e.g. VO and VI) greater than lower priority ACs (e.g., BEand BK) to determine whether a current channel may no longer besuitable.

The candidate channel assessment module 310 includes hardware, softwareand/or firmware to evaluate candidate channel suitability of at least aportion of all possible channels (possibly including the currentchannel). In one embodiment, the candidate channel assessment module 310of the AP 215 measures channel suitability metrics and communicates withthe channel agent module 230 of each STA 220 to request and obtain thechannel suitability metrics as measured by each STA 220. One or more ofthe channel suitability metrics may be on an AC-specific basis. Thecandidate channel assessment module 310 uses the channel suitabilitymetrics to generate a channel suitability index (CSI).

In one embodiment, the candidate channel assessment module 310 evaluatesonly a predetermined set of channels, possibly includes overlappingand/or non-overlapping channels. In 802.11b and 802.11g, there are three(3) standard non-overlapping channels, namely, channel 1 (2.412 GHz),channel 6 (2.437 GHz) and channel 11 (2.462 GHz) in the 2.4G Hzbandwidth in North America. Overlapping channels may include channelsbetween these channels such as channels 2, 3, 4, 5, 7, 8, 9 and 10. Atthis time, the FCC does not allow private use of channels above channel11. The candidate channel assessment module 310 may prioritize standardnon-overlapping channels over non-standard channels and over overlappingchannels.

In one embodiment, the candidate channel assessment module 310 selects afirst channel to evaluate, classifies the traffic on the channel basedon AC, obtains one or more channel suitability metrics on an AC-specificbasis, possibly obtains general channel suitability metrics, anddetermines a channel suitability index (CSI), which can be used to gradeand compare each of the channels.

In one embodiment, the candidate channel assessment module 310classifies traffic by either (a) observing the average time slot used tobegin data transmission as it is dependent on the arbitrationinter-frame spacing number (AIFSN) and the minimum contention windowsize (CWmin) values which are AC specific; or (b) observing the durationof channel busy state as limited by the transmission opportunity (TXOP)parameter which is also AC specific. By monitoring these values, thecandidate channel assessment module 310 can determine the type oftraffic being used by the STAs 220.

Generally, in one embodiment, the candidate channel assessment module310 obtains one or more AC-specific channel suitability metrics of thechannels by monitoring available channels and collecting channelutilization percentage (CU), the number of active STAs (N), the averagepacket error rate percentage (APER), and the mean received signalstrength indicator ( RSSI) on an AC-specific basis. The APER and RSSImay be fed to the candidate channel assessment module 310 by the STAs220 within the BSS 205.

In one embodiment, the candidate channel assessment module 310determines link quality (LQ) metrics per AC, weights the higher priorityAC-specific LQ metrics as more important than the lower priorityAC-specific LQ metrics, and computes a LQ parameter based on theweighted AC-specific LQ metrics. Then, the candidate channel assessmentmodule 310 determines a contention faced (CF) parameter based on thecontention that will be faced by a STA 220 joining a BSS 205 or by a BSS205 entering or moving to a channel. Further, the candidate channelassessment module 310 takes into account the impact of the number ofSTAs 220 in a particular BSS 205, since a BSS 205 with two STAs 220using 50% of channel utilization for VI traffic risks greater contentionand a BSS 205 having only one STA 220 using 50% of channel utilizationfor VI traffic. Based on the LQ parameter and the CF parameter, thecandidate channel assessment module 310 computes a channel suitabilityindex (CSI) that enables channel suitability comparison of the differentchannels.

In one embodiment, to compute the channel suitability index (CSI), thecandidate channel assessment module 420 computes the link quality (LQ)parameter as:

$\begin{matrix}{{LQ} = {\sum\limits_{{ACI} = 0}^{3}\; {\sigma_{ACI}{\Omega ( {\overset{\_}{RSSI}}_{ACI} )}}}} & (1)\end{matrix}$

where σ indicates the weight associated with a particular AC and thesubscript ACI denotes the AC index. For example, σ₀ indicates the weightfor ACI=0 (which as shown in FIGS. 1 and 5 corresponds to the AC_BE).The weights σ_(ACI) are dependent on the actual network topography. Asan example, the weights can be assigned as shown in FIG. 5. The functionΩ quantifies link robustness and is dependent on the modulation used. Asan example, assuming BPSK modulation, Ω may be defined as;

$\begin{matrix}{{\Omega ( {\overset{\_}{RSSI}}_{ACI} )} = {1 - {\frac{1}{2}{{erfc}( \sqrt{{\overset{\_}{RSSI}}_{ACI}} )}}}} & (2)\end{matrix}$

where erfc(.) denotes the complementary Gaussian error function.

The candidate channel assessment module 420 computes the contentionfaced (CF) parameter as:

$\begin{matrix}{{CF} = {\sum\limits_{{ACI} = 0}^{3}\; {\tau_{ACI}{\Gamma ( {N_{ACI},{CU}_{ACI},{APER}_{ACI}} )}}}} & (3)\end{matrix}$

where τ indicates the weight associated with a particular AC and thesubscript ACI denotes the AC index. The weights τ_(ACI) can be computedin the same fashion as shown in FIG. 5. The function Γ indicates therelative contention faced, while trying to gain access to the channel.Therefore, function Γ is dependent on the actual network topography.While it can be defined in a variety of different ways, one possibledefinition can be computed as:

$\begin{matrix}{\Gamma = \frac{\{ {( {100 - {CU}_{ACI}} ) + ( {100 - {APER}_{ACI}} )} \}}{2\; N_{ACI}}} & (4)\end{matrix}$

Thus, the candidate channel assessment module 420 computes CSI as:

CSI=Ψ(LQ,CF)   (5)

The function Ψ indicates the relative success in transmitting a packeterror free and can be defined in a variety of different ways. In oneembodiment, the function Ψ can be defined as:

Ψ(LQ,CF)=LQ×CF   (6)

The new channel selection module 315 includes hardware, software and/orfirmware to select a new channel from the set of candidate channels byusing predefined decision criteria. In one embodiment, the new channelselection module 315 selects the new channel as the candidate channelhaving the greatest channel suitability index (CSI). In anotherembodiment, the new channel selection module 315 randomly selects one ofthe channel candidates having a CSI value greater than a predeterminedthreshold. In another embodiment, the new channel may be selected fromprioritized groups, in a manner similar to that described in U.S. patentapplication Ser. No. 11/588,788 to Zhao.

The new channel setting module 320 includes hardware, software and/orfirmware to set the channel of the BSS 205 to the new channel and toinform the STAs 220 to set their channel to the new channel.

FIG. 4 is a block diagram of a channel agent module 230, in accordancewith an embodiment of the present invention. The channel agent module230 includes an AP-based analysis module 405 and a STA-based analysismodule 410.

The AP-based analysis module 405 includes hardware, software and/orfirmware that operates with the channel control module 225 to facilitatechannel suitability assessment and selection. The AP-based analysismodule 405 includes a current channel assessment agent 415, a candidatechannel assessment agent 420, and a new channel setting agent 425.

The current channel assessment agent 415 operates in a similar manner tothe current channel assessment module 305 of the channel control module225. The current channel assessment agent 415 includes hardware,software and/or firmware to communicate with the current channelassessment module 305 of the channel control module 225, e.g., to obtainthe time period T over which the current channel assessment module 505measures current channel suitability, possibly on an AC-specific basis.In one embodiment, the current channel assessment agent 415 may beconfigured to initiate current channel suitability assessment on aperiodic or substantially continuous basis. Upon detection of poorchannel suitability (e.g., average link quality lower than a thresholdor AC-specific link quality lower than an AC-specific threshold), thecurrent channel assessment agent 415 may inform the current channelassessment module 305 of the AP 115 of the poor channel suitability.

Like the current channel assessment module 305, the current channelassessment agent 415 of each STA 220 also includes hardware, softwareand/or firmware to measure AC-specific channel suitability metrics ofthe current channel (as noted by the associated STA 220). In oneembodiment, the current channel assessment agent 415 measures channelsuitability by measuring RSSI, noise, SNR, and/or the like on a per ACbasis. In one embodiment, the current channel assessment agent 415inspects the retry field in the frame header and counts the number ofretries to and from the corresponding STA 220, possibly on a per ACbasis. The current channel, assessment agent 415 of each STA 220 reportsthe channel suitability metrics to the channel control module 225 of theAP 215, which uses the channel suitability metrics to determine whetherto seek a more suitable channel.

The candidate channel assessment agent 420 is similar to the candidatechannel assessment module 310 of the channel control module 225. Thecandidate channel assessment agent 420 includes hardware, softwareand/or firmware to evaluate Ac-specific candidate channel metrics of atleast a portion of the available channels. In one embodiment, thecandidate channel assessment module 510 measures channel metrics, e.g.RSSI, noise/traffic on a channel, SNR and/or the like, of each otherchannel on a per AC basis. The set of other channels to evaluate may bepredefined or received dynamically from the candidate channel measuremodule 410. The candidate channel assessment module 510 sends the signalvalues measured to the candidate channel assessment module 310, whichuses the signal values to determine channel candidates or the mostsuitable channel.

The new channel setting agent 425 is similar to the new channel settingmodule 320. The new channel setting agent 420 of each STA 220 includeshardware, software and/or firmware to receive identification of the newchannel from the new channel setting module 320, and to set the currentchannel to the new channel.

The STA-based analysis module 41.0 includes hardware, software, and/orfirmware to facilitate selection of a BSS 205 from a set of availableBSSs 205. In one embodiment, the STA-based analysis module 410 selectsthe BSS 205 with current traffic most suitable to guarantee a high levelof QoS for new multimedia traffic. The STA-based analysis module 410includes a BSS channel assessment module 430 and a BSS selection module435.

The BSS channel assessment module 420 includes hardware, software and/orfirmware to enable the STA 220 to evaluate channel suitability metricsof each BSS 205 to determine the most suitable BSS 205. The BSS channelassessment module 420 may operate to conduct an algorithm similar to thealgorithm performed by the candidate channel assessment module 305. TheBSS channel assessment module 420 may gather the same or similarAC-specific channel suitability metrics and may apply those metrics tothe same or similar equations to generate a CSI for each BSS 205. In oneembodiment, the BSS channel assessment module 420 may query the user todetermine purpose, e.g., VoIP, streaming video, general surfing, etc. ormay just assume VI traffic. Thus, the BSS channel assessment module 420may determine which BSS 205 offers the most suitable channel. Generally,the BSS channel, assessment module 420 may choose the BSS 205 havingless higher-priority traffic, knowing, that its traffic will takeprecedence.

The BSS selection module 435 includes hardware, software and/or firmwarethat selects the BSS 205 by using predefined decision criteria, in oneembodiment, the BSS selection module 425 selects the BSS 205 having thegreatest channel suitability index (CSI). In another embodiment, the BSSselection module 435 randomly selects one of the BSS 205 having a CSIvalue greater than a predetermined threshold. In another embodiment, theBSS 205 may be selected from prioritized groups, in a manner similar tothat described in U.S. patent application Ser. No. 11/588,788 to Zhao.

FIG. 6 is a block diagram of an IBSS 600 with channel control, inaccordance with an embodiment of the present invention. The IBSS 600includes four (4) ad-hoc STAs 605 a-605 d, each having an ad-hoc channelcontrol module 610 a-610 d, respectively. Each STA 605 a-605 d may begenerally referred to as STA 605. Each ad-hoc channel control module 610a-610 d may be generally referred to as ad-hoc channel control module610. Channel control in the IBSS 600 operates in a similar manner tochannel control in the BSS network 200, except that a controller(similar to the AP 215) needs to be identified. Details of the ad-hocchannel control module 610 is described in greater detail with,reference to FIG. 7.

FIG. 7 is a block diagram of an ad-hoc channel control module 610, inaccordance with an embodiment of the present invention. The ad-hocchannel control module 610 includes a control/agent identificationmodule 705, a current channel assessment module 710, a candidate channelassessment module 715, a new channel selection module 720, a new channelsetting module 725, and a STA-based analysis module 730.

The control/agent identification module 705 includes hardware, softwareand/or firmware to enable the STAs 605 to determine which STA 605 shallact as the controller (e.g., similar to the AP 215 of the BSS network200). In this embodiment, because each STA 605 includes an identicalad-hoc control module 610, each STA 605 is capable of acting as thecontroller. The controller may be selected arbitrarily, randomly,manually, etc. The controller may be selected as the STA 220 with thefastest CPU, the largest bandwidth, the least interference, etc. Thecontroller may be selected based on serial numbers of the ad-hoccontroller module 610. A STA 220 that first determines the currentchannel fails a threshold test may become the controller. Otherpossibilities also exist.

The current channel assessment module 710 includes hardware, softwareand/or firmware to operate like the current channel assessment module305 if the STA 605 is designated as the controller and like the current,channel assessment agent 415 if the STA 605 is not designated as thecontroller.

The candidate channel assessment module 715 includes hardware, softwareand/or firmware to operate like the candidate channel assessment module310 if the STA 605 is designated as the controller and like thecandidate channel assessment agent 420 if the STA 605 is not designatedas the controller.

The new channel selection module 720 includes hardware, software and/orfirmware to operate like the new channel selection module 315 if the STA605 is designated as the controller and to be dormant if the STA 605 isnot designated as the controller.

The new channel setting module 725 includes hardware, software and/orfirmware to operate like the new channel setting module 320 if the STA605 is designated as the controller as like the new channel settingagent 425 if the STA 605 is not designated as the controller.

The STA-based analysis module 730 includes hardware, software and/orfirmware that operates like the STA-based analysis, module 410, so thata STA 605 can evaluate available BSSs 205 and select the most suitableBSS 205 to associate with.

FIG. 8 is a flowchart of a method 800 of controlling channel selection,in accordance with an embodiment of the present invention. Method 800begins with the AP 215 in step 805 tuning to a first channel. Inresponse, the STAs 220 associated with, the AP 215 associate with the AP215 by tuning to the same channel The AP 215 in step 810 determines theweights σ_(ACI) and τ_(ACI) for the different access classes anddetermines the functions Ω, Γ and Ψ. The AP 215 in step 815 monitors thechannel and traffic to determine the channel suitability metrics CU, N,APER and RSSI, possibly on a per AC basis. The AP 215 in step 820computes a link quality (LQ) parameter according to the followingequation:

${LQ} = {\sum\limits_{{ACI} = 0}^{3}\; {\sigma_{ACI}{\Omega ( {N_{ACI},{\overset{\_}{RSSI}}_{ACI}} )}}}$

The AP 215 in step 825 computes the contention faced (CF) parameteraccording to the following equation:

${CF} = {\sum\limits_{{ACI} = 0}^{3}\; {\tau_{ACI}{\Gamma ( {N_{ACI},{CU}_{ACI},{APER}_{ACI}} )}}}$

The AP 215 in step 830 computes the channel suitability index (CSI)according to the following equation:

CSI=Ψ(LQ,CF)

The AP 215 in step 835 determines if all channels to be assessed havebeen monitored. If not, then the AP 215 in step 840 switches to the nextchannel, and waits for all the STAs 220 to associate to it. Method 800then returns to step 815 to compute the channel suitability metrics forthe new channel. If the AP in step 835 determines that all channels havebeen monitored, then the AP 215 in step 845 determines the channel withthe greatest CSI value and tunes to it. The STAs 220 associate with it.Method 800 then ends.

FIG. 9 is a graph illustrating an example scenario that would benefitfrom channel control, in accordance with an embodiment of the presentinvention. As shown, of 100% channel utilization, channel #1 includes10% BE traffic and 60% VI traffic for a first BSS 205. Of the 100%channel utilization, channel #6 includes 90% BE traffic for a second BSS205. Of the 100% channel utilization, channel #11 includes 90% VItraffic. If a new STA 220 wishes to join one of the BSS 205, it canchoose from the three BSS notions.

FIG. 10 is a graph illustrating a resulting scenario after applyingchannel control on the example scenario of FIG. 9, in accordance with asystem not implementing the invention. The new STA 220 wishing to joinone of the BSS 205 of FIG. 9 might determine that channel #1 has thelowest channel utilization, and thus may join the BSS 205 using channel#1. Assuming that a streaming video request would use 60% of availableutilization, the STA 220 will be forced to share its channel utilizationwith the second STA 220 also calling for VI traffic, which currentlyamounts to 60% of channel utilization, and with the third STA 220calling for BE traffic, which currently amounts to 10% of channelutilization, BE traffic will be squeezed to a minimum 2% of channelutilization. Each VI traffic stream will be forced to share half of theremaining 98% of channel utilization, or 49% of channel utilizationeach. Accordingly, each STA 220 requesting 60% of channel, utilizationwill, be 11% deficient.

FIG. 11 is a graph illustrating a resulting scenario after applyingchannel control on the example scenario of FIG. 9, in accordance with anembodiment of the present invention. As shown, the new STA 220 wishingto join one of the BSS 205 of FIG. 9 will determine that channel #6 hasthe greatest channel suitability index (CSI), since the link quality(LQ) parameter will indicate high link quality and the contention faced(CF) parameter will indicate low contention for VI traffic. Accordingly,the VI traffic of the incoming STA 220 will assume a full 60% of channelutilization. BE traffic will use the remaining 40%. The STA 220 will notcompromise any VI traffic.

FIG. 12 is a graph illustrating an example scenario in which channelcontrol would be helpful, in accordance with an embodiment of thepresent invention. As shown, of 100% channel utilization, channel #1includes 10% BE traffic and 60% VI traffic for a first BSS 205. Of the100% channel utilization, channel #6 includes 90% BE traffic for asecond BSS 205. Of the 100% channel utilization, channel #11 includes30% BE traffic and 45% VI traffic. If an existing BSS 205 currentlyusing 10% BE traffic and 50% VI traffic wishes to select a new channel,the BSS 205 can choose from the available channels. In the illustratedexample, the BSS 205 may be currently using channel #4, which overlapsand may be currently receiving interference from the BSSs 205 of channel#1 and channel #6. The AP 215 of the existing BSS 204 may benefit fromchannel suitability assessment of each of the channels to find thechannel most suitable.

FIG. 13 is a graph illustrating a resulting scenario after applyingchannel control on the example scenario of FIG. 12, in accordance withan embodiment of the present invention. As shown, the BSS 205 selectedchannel #6, because channel #6 would likely have the best channelsuitability index (CSI). Since channel #1 has a STA 220 using 60% ofchannel utilization for VI traffic, the BSS 205 would need to compromiseits VI traffic. Since channel #11 has a STA using 45% of channelutilization for VI traffic and 30% of channel utilization, for BEtraffic, the BSS 205 would have to compromise some of its BE traffic(while it may not need to compromise any of its VI traffic). However,since channel #6 only has a STA 220 using 90% of channel utilization forBE traffic, the BSS 205 need not compromise any of its traffic.

The foregoing description of the preferred embodiments of the presentinvention is by way of example only, and other variations andmodifications of the above-described, embodiments and methods arepossible in light of the foregoing teaching. Although the network sitesare being described as separate and distinct sites, one skilled in theart will recognize that these sites may be a part of an integral site,may each include portions of multiple sites, or may include combinationsof single and multiple sites. The various embodiments set form hereinmay be implemented utilizing hardware, software, or any desiredcombination thereof. For that matter, any type of logic may be utilizedwhich is capable of implementing the various functionality set forthherein. Components may be implemented using a programmed general-purposedigital computer, using application specific integrated circuits, orusing a network of interconnected conventional components and circuits.Connections may be wired, wireless, modem, etc. The embodimentsdescribed herein are not intended to be exhaustive or limiting. Thepresent invention is limited only by the following claims.

1. A system comprising: a candidate channel assessment module forobtaining at least one AC-specific channel suitability metric for eachof two different channels, and for using the AC-specific channelsuitability metrics to determine a channel suitability index of each ofthe two different channels; a channel selection module for using thechannel suitability index to select one of the two different channels asa new channel; and a channel setting module for configuring a wirelesstransceiver to use the new channel.
 2. The system of claim 1, whereinthe system includes an access point.
 3. The system of claim 2, whereinthe access point communicates with a wireless station to obtain the atleast one AC-specific channel suitability metric therefrom.
 4. Thesystem of claim 1, wherein fee channel assessment module applies thefollowing equations to generate the channel suitability index (CSI):CSI=Ψ(LQ,CF) where Ψ indicates a function defining the relative successin transmitting a packet error free and is defined as:Ψ(LQ,CF)=LQ×CF where LQ indicates link quality and is defined as:${LQ} = {\sum\limits_{{ACI} = 0}^{3}\; {\sigma_{ACI}{\Omega ( {\overset{\_}{RSSI}}_{ACI} )}}}$where σ indicates a weight associated with a particular AC, thesubscript ACI identifies AC index, RSSI indicates a mean received signalstrength indicator, Ω indicates a function defining link robustness andis defined as:${\Omega ( {\overset{\_}{RSSI}}_{ACI} )} = {1 - {\frac{1}{2}{{erfc}( \sqrt{{\overset{\_}{RSSI}}_{ACI}} )}}}$where erfc(.) indicates a complementary Gaussian error function, CFindicates contention-faced and is defined as:${CF} = {\sum\limits_{{ACI} = 0}^{3}\; {\tau_{ACI}{\Gamma ( {N_{ACI},{CU}_{ACI},{APER}_{ACI}} )}}}$where τ indicates a weight associated with a particular AC, CU indicateschannel utilization, APER indicates average packet error rate, Nindicates the number of active STAs, and Γ is a function definingrelative contention faced when trying to gain access to the wirelessmedium and is computed as:$\Gamma = {\frac{\{ {( {100 - {CU}_{ACI}} ) + ( {100 - {APER}_{ACI}} )} \}}{2\; N_{ACI}}.}$5. The system of claim 1, wherein the channel selection module selectsthe channel having the greatest channel suitability index.
 6. The systemof claim 1, wherein the system includes a wireless station; thecandidate channel assessment module includes a BSS channel assessmentmodule; and the channel selection module includes a BSS channelselection module.
 7. The system of claim 1, further comprising a currentchannel assessment module for determining when to initiate the candidatechannel assessment module.
 8. The system of claim 7, wherein the currentchannel assessment module initiates the candidate channel assessmentmodule when a current channel link quality value fails a threshold test.9. The system of claim 1, wherein, the AC-specific metric includes anAC-specific link quality metric and an AC-specific contention-facedmetric.
 10. The system of claim 1, wherein the wireless transceiverimplements an IEEE 802.11e protocol.
 11. A method comprising: obtainingat least one AC-specific channel suitability metric for each of twodifferent channels; using the AC-specific channel suitability metrics todetermine a channel suitability index of each of the two differentchannels; using the channel suitability index to select one of the twodifferent channels as a new channel; and configuring a wirelesstransceiver to use the new channel.
 12. The method of claim 11,operative in an access point.
 13. The method of claim 12, furthercomprising communicating with a wireless station to obtain the at leastone AC-specific channel suitability metric therefrom.
 14. The method ofclaim 11, further comprising applying the following equations togenerate the channel suitability index (CSI):CSI=Ψ(LQ,CF) where Ψ indicates a function defining the relative successin transmitting a packet error free and is defined as:Ψ(LQ,CF)=LQ×CF where LQ indicates link quality and is defined as:${LQ} = {\sum\limits_{{ACI} = 0}^{3}\; {\sigma_{ACI}{\Omega ( {\overset{\_}{RSSI}}_{ACI} )}}}$where σ indicates a weight associated with a particular AC, thesubscript ACI identifies AC index, RSSI indicates a mean received signalstrength indicator, Ω indicates a function defining link robustness andis defined as;${\Omega ( {\overset{\_}{RSSI}}_{ACI} )} = {1 - {\frac{1}{2}{{erfc}( \sqrt{{\overset{\_}{RSSI}}_{ACI}} )}}}$where erfc(.) indicates a complementary Gaussian error function, CFindicates contention-faced and is defined as:${CF} = {\sum\limits_{{ACI} = 0}^{3}\; {\tau_{ACI}{\Gamma ( {N_{ACI},{CU}_{ACI},{APER}_{ACI}} )}}}$where τ indicates a weight associated with a particular AC, CU indicateschannel utilization, APER indicates average packet error rate, Nindicates the number of active STAs, and Γ is a function definingrelative contention faced when trying to gain access to the wirelessmedium and is computed as:$\Gamma = {\frac{\{ {( {100 - {CU}_{ACI}} ) + ( {100 - {APER}_{ACI}} )} \}}{2\; N_{ACI}}.}$15. The method of claim 11, further comprising selecting the channelhaving the greatest channel, suitability index.
 16. The method of claim11, operative in a wireless station.
 17. The method of claim 11, furthercomprising determining when to initiate the candidate channel assessmentmodule.
 18. The method of claim 17, further comprising initiating thecandidate channel assessment module when a current channel link qualityvalue fails a threshold test.
 19. The method of claim 11, wherein theAC-specific metric includes an AC-specific link quality metric and anAC-specific contention-faced metric.
 20. A system comprising: means forobtaining at least one AC-specific channel suitability metric for eachof two different channels; means for using the AC-specific channel,suitability metrics to determine a channel suitability index of each ofthe two different channels; means for using the channel suitabilityindex to select one of the two different channels as a new channel; andmeans for configuring a wireless transceiver to use the new channel.